A piezoelectric element can be used for an actuator, a pressure sensor, a power generator, and the like. In recent years, it has been expected to apply a piezoelectric element to energy harvesting, in which small energy in the environment generated by vibration, oscillation, and the like is harvested to be utilized. Further, it has been demanded to develop a piezoelectric element which can be used even at a high temperature. A nitride semiconductor is promising as a material of the piezoelectric element used at a high temperature, and studies regarding a piezoelectric element with nitride semiconductor have been conducted.
A film-like piezoelectric element in which a GaN layer is interposed between two AlGaN layers and a positive electrode and a negative electrode are provided to the two interfaces, respectively, is exemplified as the piezoelectric element with nitride semiconductor. However, power generation efficiency with respect to an applied voltage is insufficient in the conventional piezoelectric element with nitride semiconductor.
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